Process of extracting and recovering metals by leaching and electrolysis



Patented Oct. 13, I953 UNITED STATES PATENT OFFICE PROCESS OF EXTRACTINGAND RECOVER- ING METALS BY LEAOHING AND ELEC- TROLYSIS Robert V.Hilliard and Charles T. Baroch, Boulder City, Nev.

Application December 16, 1949, Serial No. 133,452 8 Claims. (01. 204116)(Granted under Title 35, U. S. Code (1952),

see. 266) The invention described herein may be manu- Still anotherobject of the present invention factured and used by or for theGovernment of is to provide a process whereby the alkaline rethe UnitedStates 101' governmental purposes agent solution can be regeneratedsubstantially without the payment to us of any royalty thereto itsoriginal constitution and thereby remain on in accordance with thepiovisions of the act useful for recycling thlough the process to leachof April 30 1928 (Ch 460 45 Stat. L. 467) additional quantities of oreThis invention relates to a process of t eat- Still another ob ect ofthe present invention is mg oxidized 01es or metallurgical residu sconprovide a process whereby amenable metals alkaline solution todissolve the metals, clarifyin commercial products and, at the sametime. ing the leach solution and separating it from the leave theresidual materials from leaching in a from the solutionelectrolytically, or, where sevmetals. For instance, lead, zinc, copper,when eral metals are involved, by a combination of present singly or incombination in an ore, can

' Q be removed from the ore and leave a residue process is mostgenerally amenable to the oxifrom which any gold or silver can berecovered dizedcores or products containing lead, zinc, and byflotation, cyanidation, or other known proccopper; however, other metalsare known to esses.

come under its purview. q A further object of the present invention isto Many types of ore, especially of lead, zinc, and #3 provide a processfor separating various metals copper, throughout the world are not beingexone from another or in groups which are further generally and broadlyreferred to as oxidized or from lead and copper. mixed oxide-sulfidebase-metal ores. They are generally amenable to beneficiation orconcention; clarifying, conditioning, and regenerating tration by anyknown means. Frequently the the pregnant leach solution by treating saidleach ores are complex associations of the minerals of solution withlime; removing the insoluble other and the gangue is almost impossible33 with less noble metals, independently separat- An ob ect of thepresent invention 1s to proing the thus precipitated metals,electrowmmng vide a process whereby certain metals are (2118- the basicmetallic constituents contained 1n the solved from an ore by an alkalinreagent soluresidual solution, and recycling through the leach hem and hy Separated from other step the barren solution from the electrowmningstituents of the ore. tre tment,

Another object of the present invention is to This description is givenin connectmn with process, that metal may be recovered electrolyticallyin a pure form, directly usable in the arts and industry. If the orecontains substan- Referrmg t0 the drawlng, most thoroughly oxtialquantities of two or more metals amenable idl'zed Ores are a enable totreatment by cial product. the term includes true oxides,hydrous-oxides,

carbonates, sulfates, chlorides, hydrous silicates, and similarcompounds.

Sulfide minerals are not soluble in the leaching solution, with a fewexceptions, such as arsenic, mercury, and antimony sulfides. To obtainsatisfactory extractions, sulfide or partially sulfide minerals I2require pretreatment by an oxidizing roast l3 conducted by variouswellknown means to drive off the shliur as -"aseous oxides l4.

Many artificial products may be amenable to this process, such assmelter dusts, dresses, slags, and related materials. Similarly,material for this process may be residues from other metallurgicaloperations, such as "c Some of these ieed materials may require-specialpreparation before leaching. The material must be crushed or ground to afineness consistent with good leaching practice, taking intoconsideration the physical and chemical nature of the material and themethod of leaching. Ordinarily, the feed material will need to be groundto pass a 'in'ch screen or finer, and in some cases have to bec'arriedas'fihe as minus -l-mesh to obtain good extractions.

The prepared ore or other material is charged by suitable means to theleaching operation H, where the solids are br'ought i timately in'contact with the alkaline solution L5. The method is not relevant tothe present inventhe conventional methods may as various agitationmethods, 'percolations, or heap leaching, whichever is most suitable oreconomical for a specific ore or prod- 'uct. With the exception of heapleaching, most leaching operations are condueted'in tanks, which may bemade of concrete,

solution are mi'xed or'moved with relation to each other. In agitators,the solidsand solution form a slurry kept in no tion more 'orles'sviolently by preparers; paddles or dtherfmechanical devices. thesolutron'is 116W th lbligh solids.

In percolation and heap leaching, moved by pumps an allowed to J I orfper'colate through a bed of stationary The lea Qhlng abontinuousoperation. H

The alkaline solution l'5frnay v A large variety'ofreadil'y soluble*alkalicompounds, together with'other accessory salts or compounds,dissolved in water, Theflstrong caustic alkal es sashes caustic soda, Nan, the "caustic "potash,

be made up r a non, appear t the most universanys tnfactory solvents forthe "dissolution of the largest nunittr "of metallic 'minera'ls,although solutions containing mild alkalies such as sodiumcarton-ate;mecca, potassium carbonate, KzCO3,-and -ammonium carbonate"(NI-1472003, are effective in some cases. In still other cases-a'solution of a mixture of the strong caustic and mildalkalies is mostsatisfactory. H k

The strength or "the alkali smut-10a uses for leaching may be Varied.-Within wide limits, but some minerals require stronger solutions thanothers. For instance, certai zinc minerals like sin'i'thsonite andhy'droiincite are readily soluble in solutions containing about percentstrong caustic alkali, whereas zinc silicate minerals, likeii'rnirnorphite and 'willefii'it'e may require solutions containing asmuch as 25 percent of the "'neentrator termites.

may be conducted in batches or'ln particles and the salts, such assodium chlorid same alkalies to be readily soluble under the sameleaching conditions.

Similarly the temperature and leaching time will vary with the class ofmaterial being treated. Generally, an increase in temperature isbeneficial and will permit good extractions in shorter leaching periods,and the application of heat to becomes largely an economic the morerefractory materials 4 to 18 hours at temperatures varying from 50degrees to degrees centigrade. Less refractory minerals have beenleached successiully in 2 hours at atmospheric temperatures (25 0.).Heating, when necessary, may be performed in any standard mannerconsistent with the type of leaching method. Agitation leaches areheated effectively by steam coils submerged in the leach pulp, bysubmerged burners, or electrically with heating elements. Stationary bedpercolation leache's usually require the application of heat to thesolution outside the leaching tank, that is, hot solutions are appliedto the ore be'd. Such solutions may be heated in boners,

hot-water heaters, 'or heat exchangers.

The chemical reactions involved in the dissolution of minerals "are notknown with scientific exactness, however, they are apparently 'closelyrelated to the reactions of many amphoteric ele- 'ments with basiccompounds. Lead and nine, forming compounds known as plumbite's andzinc'ates, respectively/are typical examples or the reactions involved.

I Accessory salts or the alkaline solution for the purpose of assistingin the extraction of some metals otherwise -insoluble. For instance,alkali cyanide salts may be added for the purpose of extracting gold andsilver, and certain oxidizing compounds, suchas sodium hypochlorite,N'aOCl, may be useful for oxidizing some metallic minerals. Otherneutral v p NaCl, may be added for the purpose of increasing theelectrical conductivity of the solution as well as for increasing thesolubility of minerals.

I The N leaching operation H produces a "pulp when fine ores ormaterials are leached, but a solution that can be drained away from "apercolation or heap leach.

Aiter operation 'H, the pulp or solution proceeds by suitable mechanicalarrangem'entto an operation herein designated as clarification,conditioning, and regeneration 16. The principal reagent I! used in thisopeiation'islime,"CaO,'or hydrated lime, 'Ca('OH) 2. The limehas abeneficial influence in clarifying and purifying "the "solution, anaction that may be both chemical and physical. The chemical part of theaction may be due to reactions "that are known to occur as, forinstance, the interaction of lime with the :arbonate radicals, accordingto the ioni'c equaions:

compounds may be added to Other benefits of the lime addition are more515-- jscure. For instance, it is known that the lime removeswhatappears to be dissolved 'sili'ca'from the alkaline pregnantleachsolution. "This may e a chemical decomposition of sodium silicateformed during leaching from silica in'theo're, or it may be'a physicalflocculation or agglomeration of couomn silica in the solution.Dissolved silica, at least to a certain point, isnot inimical to theprocess, but on continued recycling of solutions in a long-operatedprocess, it is desirable to have a means of controlling the silicacontent, which is performed by'the lime treatment.

at a temperature of 85 degrees centigrade, and is accelerated by hightemperatures.

It is very difiicult to removeall of these acid radical constituentsand,

CO2 per liter.

Sulfate and carbonate ions enter into the solution by the leaching anddissolution of sulfate any of a large techniques, in-

eluding filtering, settling, decantation, thickening, ntrifugmg, orcounter-current decantation, or other means or combination of methods.

cessively, each time mixing with and diluting the opposite movingthickened pulp.

The Washed solids 23 may be discarded, when tion. Otherwise such metalswould tend to codeposit with the zinc at the cathode, contaminate theresultant zinc metal, making it less useful in in lesser or traceamounts. often classed as the hydrogen sulfide group of In addition tozinc, any such metals codecation, by adding the zinc dust in portions oftion a few times, of the quantity of excess zinc the total requirement,a paucity of reactive zinc dust necessary to make a final completepurificadust surface is present while the concentration tion. Theestimated excess is then added slowly of hydrogen sulfide group metalsis highest and 10 and other quick chemical tests taken at, say 5-thenact1v1ty 1s greatest Thus, the first per minute inte vals, W111 tellthe operator when puritlons of 21110 dust have a better opportumty tocation is complete.

we st1ll have a portion or portions of fresh clean immediately at thestart of the operation to bring highly reactive zinc dust surfaces topresent In the otal concentration of these metals to around other words,by our method some highly active 2 to 5 grams per liter, and continueagitation for zinc dust is reserved for the period in the .precipaboutone-half hour Then the balance can be itation when it is most needed;the zinc dust is 20 added slowly or at intervals as above, finally,added more nearly in the ratio of the ionic recoming to the end point asdescribed above placement activity and at the rate at Wh1ch it henexceptionally large quantitles of the hydro is consumed to displace itsfull stoichiometric gen sulfide group of metals aie p esent, a longerequivalent 1n unwanted metals, and the end point lme 1s necessary forcomplete purlfication of the zinc dus The qu ck chemical t st ment1oned1s a colon- In summary, our findlngs are applied 1n a cormetric chemlcaltest based on the fact that 1f a related operat1on in step 25, asfollows A quan- 2 0 soluble sulfide 1s added to the alkaline leachsolutitv of the alkaline leach solut on is treated in 1on, dissolved mmand other metals of the hy ment to the ent1r body of liquor, yet ofinsufilsideration that forms a pure white precipitate uncient violenceto cause air to be beaten or mingled 3 der the conditions; the othersform deeply colored in bubbles with the solution. Air beaten intosulfide precipitates that have a high tinctorial,

llne solution than the unoxldized metals, thereliters in a glass testtube or beaker, to WhlCh he fore, aeration would defeat the purpose ofthe adds a drop or more of a strong solution conta nprecipitation. A o,it is preferable but not ening a water-soluble su fide, such as sodlumrely essential to perform this operat1on 1n vespotasslum or ammonlumsulfide or hydrosulfurlc efole Starting the additions of ZIIIC dust thek n 1 pr r sswely Practlcallv any mdlvldsolution is edJvsted to or nearthe opt mum temual n oon l rn t Jud h pp x m perature range of 40degrees to 50 degrees centiquantity of resldual sulfide group m tal presnt grade, heating or cooling, as the case may be If and can discern whenthe prec1p1tat1on of thes necessary. T e zinc dust can be added 1nmeasmetals Completeured batches with a time interval between batches Incalculating the stoichiometric requirement or it may be added slowlybut; continuously by a of zinc dust it must be borne in mind that allzinc proper type of feeding device. The time interval ust contains somezinc oxide, and it is only the cases .for making use of uncommercialgrades of zinc dust as, for instance, types of metallurgical productsknown in trade as blue powder and which are frequently difiicult toreprocess or beneficate into commercial-grade products. Needless to say,all zinc dissolved in this purification step enters the zinc electrolyteand is recoverable in the subsequent electrolytic precipitation.

The amount of excess zinc dust required cannot be predicted with extremeexactness, as this will depend largely on the careiulness of theoperator in estimating and approaching the end point of purification.Careful, but not overmeticulous operation, should give the degree ofpurification required by using an excess amount of metallic zinc dustequivalent to about 0.1 gram per liter, or slightly under 1 pound ofzinc dust per 1,000 gallons of solution, if the directions of thisspecification are followed. This, on 1,000 gallons of a leach solutioncontaining 10 grams Pb per liter, for instance, which requires 26.3pounds of zinc dust to stoichiometrically precipitate the lead, wouldamount to slightly over 3 percent excess or 103 percent of thestoichiometric zinc dust required. These figures are cited as an exampleof good practice but it is not intended that this disclosure should belimited strictly to the figure cited, because it is evident that, in theexample given, an excess of zinc dust possibly more than ten-fold thatshown, could be deemed to be economically practicable.

After the hydrogen sulfide group of metals have been precipitated to theproper degree of completeness, the solution should be separated asquickly as possible from the precipitated metals. Decantation or vacuumor pressure filtration or a combination may be employed, prefer pressurefiltration whereby the slurry is withdrawn from the bottom of theprecipitating vessel by a pump and forced through a pressure filter,because no air is mixed with the solution which can cause oxidation ofthe precipitated spongy metals and re-solution in the alkaline Thepurified zincate electrolyte 28 now passes on to electrolysis, step 29,and the spongy metal precipitate can be washed while in its firstfilter-cake form or it may be washed more elaborately as one chooses. Inany case, we find it is preferable to segregate purified zincelectrolyte from washings, returning the washings to the next batch ofleach solution entering the purification step 25, thereby preventing anypossible redissolved spongy metals from contaminating the zincateelectrolyte. If the purification has been conducted with a minimum ofzinc dust by the procedure outlined herein, the washed spongy metal,after drying, contains only slight amounts of zinc and consistpredominantly of hydrogen sulfide group metals, Their furtherbeneficiation, purification and melting can be accomplished byestablished procedures well known to the art.

Alternatively, especially when large amounts of hydrogen sulfide metalsare present, it may be desirable to perform their precipitation in twoor more stages on the countercurrent principle. In the first stage, thehydrogen sulfide group of metals could be precipitated to a lowconcentration remaining in the solution; the precipitate in this stagecould be removed by filtration and would be substantially free of zinc,The solution'would proceed to a second stage where the residual hydrogensulfide group of metals could be removed completely with an excess ofzinc dust; the filtrate from this stage would be purified electrolyte,while the precipi-- tated sponge would .be relatively high in mm. Thisprecipitate, obeying the countercurrent principle, would be charged backto the first stage where the high concentration of hydrogen sulfidegroup metals would attack and remove the residual zinc from thesecond-stage precipi- The metals of the hydrogen sulfide group belowzinc in the electromotive force series of elements may also be removedseparately by precipitation in a step wise manner. For example, where analkali cyanide is used as an accessory salt in the alkaline solution forextracting precious metals during the leaching operation, these preciousmetals represented by gold and silver, can be precipitated from thesolution by means of metallic copper to produce a soluble removablesludge of gold and silver. The residual solution may then be contactedwith finely divided or sponge lead for precipitation of copper. Afterremoval of the copper, the solution is then treated with electrolyticflake zinc to precipitate metallic lead and any remaining metals belowzinc in the electromotive force series of elements under the conditionsdescribed above.

The purified zinc electrolyte or zincate solution 28 proceeds to thenext step, precipitation of zinc by electrolysis 29.

Electrolysis may be conducted in cells of any convenient design, themain essential of a cell being a group of plane surfaced electrodessupported or suspended in a body of the electrolyte so that a directelectric current may pass between one or a group of these electrodes,called cathodes, to a pair or more of other electrodes, called anodes.Conveniently, a plurality of electrodes are usually placed in a box-liketank, alternating anodes with cathodes, which are spaced more or lessevenly and parallel. Ordinarily, diaphragms between anodes and cathodesare not necessary. The electrolyte may be agitated or still; usually acontinuous flow of electrolyte enters one end of the cell while depletedor partially depleted electrolyte overflows at the other end.Electrolyte may pass successively through a group or cells or each cellmay have individual electrolyte infiow and outflow, as desired. Usually,several cells are in electrical series to conform with good engineeringpractice in electrical circuits, that is, to provide a good balancebetween voltage and amperage in the direct-current electric supply. a

The tanks for cells may be constructed of any structural material whichwill withstand the alkaline electrolyte. Iron, steel and nickel areexceptionally good materials for this purpose, however, if the highestpurity of zinc is desired a nonmetallic surface is best to preventcontamination of the zinc, and glass, rubber, or synthetic plasticlinings of these metals is advantageous.

The cathodes may be practically of any metal which will not dissolvereadily in the alkaline electrolyte, and they may be made of rolledsheet or cast metal. Iron, all varieties of steel and ferroalloys,nickel, zinc, magnesium, and magnesium alloys are the most desirable,although others, such as carbon, graphite, copper, bronze, brass, andthe precious and rare metals are suitable.

The anodes are subject to strong oxidation during electrolysis,therefore, choice of anode material is limited to those elements whichare 5 very diflicult to oxidize orwhose oxides are iniron, steel alloys,practical of The voltage required per cell to deposit metal will varyprincipally with the temperature, the spacing between anodes andcathodes, and the current density. Using a typical zincateelecpurification, powder deposition is especially efiective at cathodecurrent densities varying from 80 to 5 grams Obviously, both solid plateand dust can be produced by different cells electrolytic circuit, if

A periodically and scraping them, or by using highly polished will notadhere telimits can be controlled without spirit and scope of thepresent invention. The physical nature of the zinc recovered withinwhich such accordance with our detailed description, prodeparting fromthe tion I l.

A typical operation in practice of the process described by the presentinvention is exemplified by the leaching of an oxidized zinc-lead ore,having the following analysis:

for 12 to 16 hours and a clear solution decanted from a. pulp containingabout 20 percent undissolved solids.

a pressure filter and washed with water (step 2|).

original ore, due to dissolved minerals, and a typical dried residue 21contained the following residual metals:

Per cent Zn 6.16 Pb 0.0004 Cu 0.064

the zinc; 99.0 percent of the lead; and 84.7 percent of the copper.

The ore also less than 0.01 ounce of gold per ton. In part of the basemetals.

The solution 2! combined with washings 24 proceeded to s ep copper,

dust 26. is purification was conducted in a tank equippedwith amotor-driven propellertype agitation The temperat. re;v was about '40":degrees, centigrade, and: zinc. dust. was added: slowly in smallportions; at. intervals; of about. 15,; minutes until the rapid.qualitatiye: chemical; test; described detail: above; showed that thesolution; no longer contained significant. amounts" or lead'; orcopper;The, zinc;- dust usedwas: elec trolytic flake zincproduced: by this sameprocess. and the stoichiometric' amount: of metallic zinc: required, bythe leach solution was; 0A9 gram per liter. The precipitation consumedfrom 0;.65 to; 0 .510 gram; of flake: which had a metallic zinc contentor about. 94 percent; therefore, the actual precipitation required: from0.61 to 0.66; gram of metallic zinc per liter, or an excess of 0.12; to01"! gram per liter.

Pmification. time. ordinarily required. from. to 2 hours. andv then themetal precipitate 21. was separated from the. purified zincate solution28 by filtration.

Typical dried metal precipitate 21 analyzed follows; V i

Per cent Pb V ,warmer- 52.1 Zn 13.8 Cu 6.0,

the tests in which sodium cyanide: had been added for recoverycf theprecious metals, similar precipitates were recovered which alsocontained ounces of; silver per ton and 0.0 ounce of gold. The ratio ofconcentration of the lead and copper is, of the-order of i6 into 1 andanyoneversed in the art will recognize the vastly superior commercial.qualities of this precipitate.-

comparedhe-originalorm The purified zincat'e solution, 28;, now readyfor electrolysis analyzed as follows:

Gram-s per liter zir r s r l 3716 to 42.6

Pb- 0.000s Cu: 0.002s Fe 0.004

The high, purity obtained and the extremely low ratio of other metals tozinc will be apparent to one skilledi-n the art.

Electrolysis 29 was conducted in a rectangular cell with a hopperbottom, constructed oi mild sheet steel and paintedonthe interior withPlastic paint. All types of cathode material men-- tioned in the generalspecification. above were found to be suitable; magnesium alloy wasespecially satisfactory for producing flake dust, and stainless steelappeared to be slightly more ravorable in producing solid plate metal,Anodes of all types mentioned in the general specification were usedsatisfactorily; as nickel and mild steel are the most resistant metalsto caustic solution, they would be best in commercial practice and theminute amounts of their corrosion products would be least harmful to thezinc. Stainless steel worked well, especially after con-. ditioning forseveral hours in electrolyte as an anode. The cell for the tests in theexample contained two cathodes and three anodes.

Solid plates were produced at current densities between and 50 amperesper square foot and an electrolyte temperature of 80 degrees centigrade.Electrolytic flake zinc was produced at around 40 degrees centigrade andat; amperes per square foot and as high as 200 amperes per square foot;especially good results were obtained at. current densities between 80and 120 amperes per square foot. At 80 amperes per square foot, currentefficiency was above 80 percent and power consumptioniwas about.1.2:.kw;.-hr.\of direct cur rent energy per pound of flake: zincdeposited Power consumptionincreased slightly as-thecnre rent densitywasraised.

Flake zinc produce 1 analyzed better thanv 99.10?- percent Zn and betterthan 94.0 percentmetallic: Zn;v the difference, calculated accordingtoestandard methods ('diiierence times L244T=Zn0lg meantv thatlessthanfi percent ZnO was genera ally present. Other metallicimpurities analyzed: as follows, typically;

Per cent:- Pb. 0.0702;- Cu 010(15- Fe. 01120 Purified electrolyte wasfed to the cell atv such a rate that the overflow of the cell, ordepleted electrolyte 30 contained from 4.6 to. 1015 grams, n per liter.thus r co g tram Q to nert' f the in fr m the. purifie lectr lyte... Thebalance, of course, was not lost, as it, recycled in the leaching ofadditional ore.

The solution was recycled eight times without. regeneration orconditioning, step it. The, electrolyte during this time graduallybuilt, up to 2.8 grams S102. and 53 grains 0.0 per liter. At, this.point conditioning with lime was. injected into the next cycle, and thesolution was lowered to 1.9 grams S102 and 22. grams C Qz perliter,

The principal advantages oi. the process described by the presentinvention are: (1') It pro.- vides a process for treating certainlow-grade, complex, or refractory ores, which cannot be treated by otherknown methods economically; (2') it provides a process for treating,efficiently and economically certain other ores, which are now beingtreated by known methods in. an inchicient and expensive. manner; (3) itprovides a process for recovering additional metal values, fromfwasteproductes or tailings. resultin from processes in which the oxidizedmetals or poitions of the metallic values are in an oxidized form; forinstance, oxidized copper and zinc. minerals are not readily amenable torecovery by flotation processes and the unrecovered portion of theseminerals could be recovered by the pres.- ent invention; (4) it providesa process for treat.- ing certain ores for the recovery of metalsamenable to this process and leaves the residue comparatively unaltered,but generally beneficiated to some extent, so that this residue can beused 'for recovery of other metals; for instance, in a highlyferruginous oxidized lead-zinc ore, the lead and zinc could beextracted, leaving a resi due which might be suitable for use'as an ironore; and (5) it provides a means of treatingv oertain calcareous oralkaline. ores which are. costly or impossible to treat by presentwell-known acidv leaching methods because of the high consumption, ofacid required for their dissolution.

Since many widely difiering embodiments of the invention will occur toone skilled in the art, the invention is not limited to the specificdetails illustrated and described, and various changes. may be madetherein without departing from the spirit andv scope thereof.

What is claimed is:

l. The method for the separation and recovery of metallic constituentsof oxidized lead-zine ores. which contain other metals including gold,silver, and copper, in. addition to lead and zinc which comprises thesteps, of leaching the oxidized ore in an alkali-cyanide. solution;treating the preg: nant leach solution with lime; removing the in-,soluble residues from the thus treated solution;

displacing the gold and silver in the solution with 5. The method forthe separation and recovery metallic copper; separating the precipitatedgold of metals from oxidized lead-zinc ores containmetal and silvermetal; displacing the copper ing other metal which comprises leachingthe from the solution with metallic lead; separating oxidized ore with astrong alkaline solution conthe precipitated copper metal; adjusting thetaming from about 5% to about 25% of caustic temperature of the solutionto about 35 to about alkali, treating the hot pregnant solution with 50C., displacing lead and any remaining metals lime, removing theinsoluble residues from the below zinc in the electrolnotive forceseries of thus treated solution, displacing metals other elements bycontacting the solution with electrothan zinc from the solution at atemperature of lytic flake zinc, immediately removing the metal about 35C. to about 50 C. by contacting the precipitate from solution;electrowinning metalsolution with electrolytic flake zinc, immediateliczinc from the alkaline solution from which 1y removing the metalprecipitate from the soluthe more noble metals have been sepa ated andon, electrowlnnin metallic zinc in substanrecycling the barren alkalinesolution to the leach 'tially pure form from the remaining puritep, fiedzincate solution, and recycling the regen- 2 The method for t eparatignand 'egovery erated barren solution of strong alkali to the of metallicconstituents of mixed-oxide-lead-zinc leaching step. ores which containother metals including gold, The method o the p ra o a d c v y silver,and copper, in addition to lead and zinc of metals from oxidizedlead-zinc ores containwhich comprises the steps: of leaching the mixedmeo h r m als whi h mpr l ach n th the pregnant leach solution with lime;removing about With a stron alkaline solution conthe insoluble residuesfrom the thus treated solutaming m about 5% to about of caustic tion;displacing the gold and silver in the soluali, adjusting the temperatureof the solution tion with metallic copper; separating the precipi- 25 tofrom about to ab 5 d splacin t b t 50 displamng l and any remaintodisplace all or the other metals from solution oretically required todisplace said metals has the regenerated barren Solution of stro galkali been added, immediately removing the metal to l a hme step.

precipitate from the solution; electrowinning The method f r theseparation and recovmetallic zinc from the alkaline solution from metalsfrom oxidized lead-Zinc ores con- Which the mole noble metals have beensepa taming other metals which complises leachlng rated; and recyclingthe barren alkaline solution 40 the Oxidized Ore at a mperature of about50 C. to the leach Step to about 80 C. with a strong alkaline solution3. The method for the recovery of zinc from Containing from about toabout 25% of causoxidized inc ores ontaining other metal in alkali,treating the Qt pregnant Solution eluding lead and zinc which comprisesleaching hme, removing 'i nsoluble residues from the the oxidized orewith a strong alkaline solution, thus sated Solution, l mg thetemperature until slightly more than that amount of zinc rer than hELmount f nc required theometals fmm the Solution has been added 1mmesolutlon has been added, immediately removing djately removmg the meta]precipitate from the the metal precipitate from the solution elecrosolutlon electrowlnnlng metallic zinc in substan- Wmnmg metaulc Z1110111 Substantially pu e form barren solution to the leaching step. strongalkali t0 the i g Step.

4. The method for the separation and recovery The method Q theSeparation and recovery of metals from oxidized lead-zinc orescontaining P metals from Wildizecl d-zinc ores containother metalsincluding gold, silver and copper f metals {ncludlng gold, Sliver, a doopwhich comprises leaching the oxidized ore with a Whlch comprlsesleaching e oxidized ore strong alkaline solution to which a small quanata temperature about to about o. my of alkali cyanide has been added towith a strong alkaline solution containing from rently extract the goldand silver, treating the about 5% to about of u ic alkali and todisplacing the metals other than zinc from the trfgatmg h hot eenaetSolution With lime, solution at a temperature of about 35 C. to aboutremoving msoluPle res1dues from the thus 50 o. by contacting thesolution with electrolytic treated sPlutlon adlustlne' the temperatureof flake zinc, immediately removing the metal pre- 7 the solutlon toabout C. to d p acing maining purified zincate solution and recyclinginc added in small increments until slightly-more the regenerated barrensolution to the leaching than that amount f Zinc quired theoretically t7 to displace all of the other metals from the solution hasbeen-added;Jmniediately removiiig the metal precipitate from thesolutiorr, 'eleetrowinning metallic zinc'in substantially pure form fromthe'remainin'g purifiedzincate solution; amine v cycling theregenerated-barrensolution of strong alkali 120 the leaching step.

ROBERT V. HILLIARD; CHARLEST. BAROCH.

References: Cited, in the file "of this patent UmTEDsT-A'riis PATENTSNfi'inberr Date Ketchum Oct. 19, v189? Number m Number 415,639 24, 21Quasi

1. THE METHOD FOR THE SEPARATION AND RECOVERY OF METALLIC CONSTITUENTSOF OXIDIZED LEAD-ZINC ORES WHICH CONTAIN OTHER METALS INCLUDING GOLD,SILVER, AND COPPER, IN ADDITION TO LEAD AND ZINC WHICH COMPRISES THESTEPS OF LEACHING THE OXIDIZED ORE IN AN ALKALI-CYANIDE SOLUTION;TREATING THE PREGNANT LEACH SOLUTION WITH LIME; REMOVING THE INSOLUBLERESIDUES FROM THE THUS TREATED SOLUTION; DISPLACING THE GOLD AND SILVERIN THE SOLUTION WITH METALLIC COPPER; SEPARATING THE PRECIPITATED GOLDMETAL AND SILVER METAL; DISPLACING THE COPPER FROM THE SOLUTION WITHMETALLIC LEAD; SEPARATING THE PRECIPITATED COPPER METAL; ADJUSTING THETEMPERATURE OF THE SOLUTION TO ABOUT 35* TO ABOUT 50* C., DISPLACINGLEAD AND ANY REMAINING METALS BELOW ZINC IN THE ELECTROMOTIVE FORCESERIES OF ELEMENTS BY CONTACTING THE SOLUTION WITH ELECTROLYTIC FLAKEZINC, IMMEDIATELY REMOVING THE METAL PRECIPITATE FROM SOLUTION;ELECTROWINNING METALLIC ZINC FROM THE ALKALI SOLUTION FROM WHICH THEMORE NOBLE METALS HAVE BEEN SEPARATED; AND RECYCLING THE BARREN ALKALINESOLUTION TO THE LEACH STEP.